Two-stroke engines have many advantages over four-stroke engines. One distinct advantage is that two-stroke engines have far fewer movable parts than four-stroke engines. Another advantage is that the fuel is combusted each time the piston reaches the top of the cylinder, i.e. a working stroke takes place with each revolution of the piston, via the crankshaft coupled to the piston rod.
One drawback of two-stroke engines is that the combustion of the fuel mixture is poor due to the fact that fresh fuel mixture is delivered to the cylinder at the same time as the exhaust gases are ventilated. This results in non-combusted fuel mixture departing with the exhaust gases.
The most common type of two-stroke engines includes passages for conveying the fuel mixture into the cylinder space in the cylinder wall at a distance from the cylinder combustion chamber that slightly exceeds the distance from the combustion chamber to an exhaust port in the cylinder wall. When fuel is combusted in the combustion chamber, the piston moves downwardly and the upper surface of the piston will thus first pass the exhaust port so that the exhaust gases flow out the port. The upper surface of the piston will then pass the passageways through which fuel mixture flows into the cylinder. However, this inflow of fuel mixture takes place while the exhaust port is still open. As the piston moves upwardly, it will first pass the passageways that are closed and thereafter pass the exhaust port so as to close the same. A certain portion of the fuel mixture will be pressed out through the exhaust port, partly while fuel mixture is being injected into the cylinder and partly during the upward movement of the piston.
This problem may be avoided by directly injecting fuel through the cylinder head of the engine, and by injecting air into the cylinder, via a valve mounted in the cylinder head, subsequent to the exhaust port having been closed by the piston as it moves up in the cylinder. However, this solution requires providing the engine with electronic means for controlling the injection nozzle and also with a compressor for delivering the combustion air.
The present invention solves the problem of achieving a high degree of combustion in two-stroke engines without requiring additional movable parts or other control equipment for delivering a fuel mixture. The two-stroke internal combustion engine of the present invention includes a cylinder, a piston, a connecting rod connected between a crankshaft and the piston, a crankcase inlet for fuel mixture from a carburetor, a passageway defined between the crankcase an induction or inlet port in the cylinder wall, and an exhaust port in said cylinder wall. The exhaust port communicates with the surroundings so that a cylinder is common to two oppositely moving pistons. Crankcases are provided at both ends of the cylinder so that each crankcase includes a crankshaft which is connected to respective pistons via a piston rod and so that the crankshafts are interconnected mechanically. In this way, both pistons may move simultaneously to their top center positions and also move simultaneously to their bottom center-positions. A carburetor is connected to the first crankcase. An important feature is that only the second crankcase is connected to the induction port via a passageway. The exhaust port is positioned for coaction with the piston belonging to the first crankcase. A pipe extends between the first crankcase and the second crankcase for transporting the fuel mixture from the first crankcase to the second crankcase. A check valve is provided between the first crankcase and the inlet end of the pipe.